A recent check of the rapid test used in the UK is that its largely unaware of the virus if the necessary PCR cycles are > 25, gets it right half of the time for CT between 20 and 25 and it gets very good if viral load is large enough to be detected by < 20 cycles. Other rapid tests are AFAIK somewhat better.
The main problem that most (western) countries failed to solve is to remove reasons to not take a test and not to self-isolate, and that's primarily inability to get proper support WRT work / monetary situation while self-isolating.
Make it easier for people to self-isolate than not to, and people will do it.
https://advances.sciencemag.org/content/early/2020/11/20/sci... https://www.medrxiv.org/content/10.1101/2020.06.22.20136309v... (preprint of above)
I have friend who has a colleague who always produces a false pos. antibody test. They know it, they still test him. (At this point basically to make sure the test does something at all.)
After all, every kind of proactive/preventive measure helps a bit to keep a group/family/workplace safe.
Unless you are also worried about false negatives you only need to perfrom the better test on those that reported positive on the quicker test.
Exactly for this reason.
It's not perfect. PCR can miss the early stages of the infection too.
These are just signals.
Luckily we know that viral load is the factor for transmission rate (infectiousness). So even if someone is (false) negative, but has symptoms, should self-quarantine.
That assumes that for each test it is a sort of dice roll on whether or not there will be a false result. It might be that something about the individual person's biochemistry or health history (like prior exposure to a different corona strain) is the cause of the false result. If that's the case, then people who receive a false result on this type of test will tend to always receive false results, and testing more often won't help much.